A barrier infrared sensor can detect any movement that passes the infrared light beam, is currently widely used as invisible fence for walls and alarms. This is a barrier Infra-red short-range use as an alarm for doors and gates. Virtually any infra-red LED can be used, therefore it becomes easy to build.
The 555 Transmitter (figure above) oscillates around 4,5 kHz, providing pulses with a duty cycle of about 13%, this to keep power consumption within acceptable standards. The exact pulse frequency is adjusted with P1.
At the receiver (Figure below) , the maximum sensitivity of photo-diodes D2 should occur at a wavelength of IR LEDs used in the transmitter. Recommended use SFH205F, BPW34 or BP104. Note that the photo diode is connected in reverse bias. Then, if you measure about 0,45 Through this device V, is almost certainly that is mounted the wrong way.
The received pulses are amplified, then, comes a PLL (phase lock loop), Built with NE567. The chip PLL, low when it is locked in “tone” of 4,5 received from the transmitter kHz. When the light beam is interrupted, the received signal disappears and IC1 will have a high output, thus triggering the alarm.
If the transmitter is too far away from the receiver, over-driving will no longer be guaranteed, hence IC1 will not activate, if you want to get the most out of the loop regarding the distance, Start by modifying the R2 value until the output signal of the amplifier again has a cycle of about 50%.
The circuit is simple to adjust. Connect the receiver, the buzzer should sound. Then, turn the transmitter. Point transmitter LEDs to the receiver input. Use a relatively small distance, say, 30 cm. Adjust P1 on the transmitter until the bell is silenced. Turning off the receiver and reconnect a few times to make sure it locks into carrier transmitter in all circumstances. If necessary, P1 readjust, slowly increasing the distance between the transmitter and receiver.